Steady Cycles Research Articles

Performance characterization of a selective catalytic reduction on filter aftertreatment system in a heavy-duty diesel engine tested on a laboratory dynamometer

Increasingly stringent emission regulations call for improvement in the current emissions control technology in heavy-duty diesel engines. In the existing aftertreatment system utilized in diesel engines, there is already a challenge with space and volume, and an attempt to add more components would lead to the consumption of more space and impracticable. The Selective Catalytic Reduction on Filter (SCRF)-an integration of Selective Catalytic Reduction (SCR) and Diesel Particulate Filter (DPF) in a single component, offers space saving and favorable thermal inertia opportunities. However, literatures are conflicting on the effect of the SCR and DPF activities on the operations of the SCRF, as both require NO2 for fast SCR reaction, and passive soot oxidation respectively. This paper presents a detailed experimental characterization of a Silicon-Carbide (Si–C) coated with Copper-Zeolite (Cu-Ze) catalyst SCRF after-treatment component in a heavy-duty diesel engine, evaluated on a laboratory dynamometer. The effect of particulate matter loading on the SCRF activities in steady state, and transient operations was investigated, with emphasis on the simultaneous utilization of NO2 between the passive soot oxidation activities and SCR reactions-which is a determinant of the NOx conversion efficiency. The SCRF was loaded from 0 g/L up to 5 g/L while passive regeneration and NOx conversion activities were investigated over steady and transient cycles. The investigation has shown that both NOx conversion efficiency and passive soot oxidation increase with particulate matter loading in the SCRF system of a heavy-duty diesel engine.

Thermal management of electronics from −40 °C to 150 °C enabled by hydrate salt composite with efficient thermal energy storage

Integration and miniaturization of electronic devices means efficient thermal management is urgently required. In this paper, thermally conductive but electrically insulated boron nitride (BN) is strung by polyacrylonitrile (PAN) fibers to form a flexible and porous BN@PAN film. Subsequently, solution impregnation combining cold pressing is used to fabricate sandwich-like structure SAT/BN@PAN (SBP) that alternately layered by hydrate salt sodium acetate trihydrate (SAT) and BN@PAN film. The flexible and electrically insulated SBP film possesses high leakage-proof temperature and latent heat. Meanwhile, the sandwich-like structure increases in-plane thermal conductivity by 20 times thus largely promotes anisotropic heat transfer. Consequently, the SBP film heats electronics by 10 °C at −40 °C via heat release from solidification maintaining its steady working cycles. More importantly, the SBP film can suppress overheating by 50 °C at 150 °C via melting and thermal chemical reaction indicating potential in thermal runaway prevention. The wide-range (-40 ∼ 150 °C) thermal management capability and simple fabrication technique of the sandwich-like SBP film provide application potential in advanced electronics devices.

Phosphate Ester Bond Chemistry with Zirconium (IV) Catalysts

Earth’s infancy was a time of immense chemical complexity. Over many millions of years, steady chemical cycles were formed and driven by thermodynamics and organic precursors left over from the planet’s formation. In aqueous environments, this chemistry may have led to the formation of catalytic RNA species capable of information storage and replication. Presumably, the formation of these oligonucleotides was catalyzed by primordial Earth’s abundant mineral content. However, the species that accelerated these types of transformations are unknown. In this study, the role of Zr+4 in the catalytic formation of phosphate ester bonds was explored. Through TLC screening, it was found that most of the test conditions produced no observable phosphorylated products. In the final samples, there were highly polar spots which may have contained phosphate-bearing compounds. These findings provide mixed certainty about zirconium’s catalytic capacity for ester formation but suggest that zirconium metal organic frameworks (MOFs) and alternative metal ions may be viable routes for future investigation. Lay Summary Earth began as a planet of rock and magma, hardly recognizable without the biological adornments that characterize it today. For nearly a billion years, consistent comet and asteroid impacts heated the planet and vaporized any reservoirs of water or organic matter that covered the surface. As this bombardment subsided, life came to fruition in half the time that the mineral rain had lasted. The question of how this transition occurred is one of the most elusive in the biochemical field. In particular, it is still unknown how all life, whether primordial or modern, came to share polynucleotides as an essential coding system for all their requisite biological functions. This study explored the role of Zr+4, an abundant mineral on early Earth, in the catalytic formation of phosphate ester bonds, the core linkages in DNA and RNA. Through TLC screening, it was found that most of the test conditions produced no observable phosphorylated products. In the final samples, highly polar spots may have contained phosphate-bearing compounds. These findings provide mixed certainty about zirconium’s capacity for ester formation but suggest that zirconium metal-organic frameworks (MOFs) and alternative metal ions that reflect early Earth’s composition may be viable routes for future investigation into this grand mystery. To see the complete thesis, please visit https://scholar.colorado.edu/concern/undergraduate_honors_theses/cf95jc857.

Steady and oscillatory flows generated by Eckart streaming in the two-dimensional Rayleigh–Bénard configuration

This paper presents a detailed analysis of the flows induced in a long two-dimensional cavity heated from below in the presence of streaming due to ultrasound acoustic waves emitted by a source. The problem is tackled by using performing spectral element codes, allowing continuation of steady solutions, bifurcation points and periodic cycles. For a given dimensionless source size, the governing parameters are the acoustic streaming parameter $A$ which modulates the acoustic force generating the Eckart streaming and the Rayleigh number ${\textit {Ra}}$ which quantifies the buoyant force responsible for the convection. The streaming flow, which goes to the right along the horizontal axis and returns along the lower and upper boundaries, influences the instability thresholds, which are first strongly stabilized above the pure Rayleigh–Bénard threshold ${\textit {Ra}}_0$ when $A$ is increased, before a destabilization to reach the pure streaming threshold $A_c$ at ${\textit {Ra}}=0$ . The steady multi-roll convective flow generated without streaming is replaced by periodic waves when $A$ is increased, forward waves for moderate $A$ and backward waves for large $A$ . The transition between these waves induces a specific dynamics involving steady flows, which has been elucidated. The waves also eventually disappear for a sufficient increase of the Rayleigh number, replaced by steady multi-roll flows hardly influenced by the streaming flow. A very rich dynamics is thus observed with the competition between the waves and the steady flows.

Can neural networks predict steady annual cycles of marine ecosystems?

We used artificial neural networks to replace the complete spin-up procedure that computes a steady annual cycle of a marine ecosystem driven by ocean transport. The networks took only the few biogeochemical model parameters and attempted to predict the spatially distributed concentrations of the ecosystem, in this case only nutrients, for one time point of the annual cycle. The ocean circulation was fixed for all parameters. Different network topologies, sparse networks, and hyperparameter optimization using a genetic algorithm were used. This showed that all studied networks can produce a distribution that is point-wise close to the original spin-up result. However, these predictions were far from being annually periodic, such that a subsequent spin-up was necessary. In this way, the overall runtime of the spin-up could be reduced by 13% on average. It is debatable whether this procedure is useful for the generation of initial values, or whether simpler methods can achieve faster convergence.

ACCOUNTING THE EMISSIONS OF ENGINE FUEL VAPORS IN THE CRITERIA-BASED ASSESSMENT OF THE ECOLOGICAL SAFETY LEVEL OF POWER PLANTS WITH RECIPROCATING ICE EXPLOITATION PROCESS

This study proposed the approach and method on its basis for carrying out of the calculated assessment of the values of the comprehensive fuel and environmental criterion of Prof. I. Parsadanov as the indicator of the ecological safety level of the exploitation process of power plants with diesel reciprocating internal combustion engine, considering the mass hourly emissions of engine fuel vapor caused by the phenomena of large and small breathing of reservoirs. The purpose of the study is to develop the method for taking into account the parameters of pollutant emis­sions into the environment, such as motor fuel vapors due to the phenomena of large and small breathing of the power plant fuel tanks, as an independent factor of ecological safety. The calculated assessment according to the proposed method is carried out considering the properties of engine fuel, degree of a fuel tank filling, features of model of the engine operation, daily difference of atmospheric air temperature and settings of the respiratory valve of the tank. It is found that considering the emission of engine fuel vapors caused by the phenomenon of small breathing has almost no effect on the level of environmental safety, but for the option of taking into account the effect of the phenomenon of large breathing, such an effect is significant. The scientific novelty of the obtained results is that for the first time a method for considering the emission of engine fuel vapors caused by large and small breathing of fuel tanks of reciprocating internal combustion engines in complex criteria-based assessment of ecologi­cal safety. The practical value of the obtained results is that they are suitable for quantitative and qualitative assess­ment of the studied effects and development on this basis of technical solutions and organizational measures to redu­ce or eliminate them by developing appropriate environmental protection technology with actuators on a me­thodological basis of environmental safety management system, including the use of other steady standardized testing cycles as models of engine operation.

Topologically protected steady cycles in an icelike mechanical metamaterial

Competing ground states may lead to topologically constrained excitations such as domain walls or quasiparticles, which govern metastable states and their dynamics. Domain walls and more exotic topological excitations are well studied in magnetic systems such as artificial spin ice, in which nanoscale magnetic dipoles are placed on geometrically frustrated lattices, giving rise to highly degenerate ground states. We propose a mechanical spin-ice constructed from a lattice of floppy, bistable square unit cells. We compare the domain wall excitations that arise in this metamaterial to their magnetic counterparts, finding that new behaviors emerge in this overdamped mechanical system. By tuning the ratios of the internal elements of the unit cell, we control the curvature and propagation speed of internal domain walls. We change the domain wall morphology from a binary, strictly spin-like regime, to a more continuous, elastic regime. In the elastic regime, we inject, manipulate, and expel domain walls via textured forcing at the boundaries. The system exhibits dynamical hysteresis, and we find a first-order dynamical transition as a function of the driving frequency. We demonstrate a forcing protocol that produces multiple, topologically-distinct steady cycles, which are protected by the differences in their internal domain wall arrangements. These distinct steady cycles rapidly proliferate as the complexity of the applied forcing texture is increased, thus suggesting that such mechanical systems could serve as useful model systems to study multistability, glassiness, and memory in materials.

3D FE-Informed Laboratory Soil Testing for the Design of Offshore Wind Turbine Monopiles

Based on advanced 3D finite element modelling, this paper analyses the stress paths experienced by soil elements in the vicinity of a monopile foundation for offshore wind turbines subjected to cyclic loading with the aim of informing soil laboratory testing in support of monopile foundation design. It is shown that the soil elements in front of the laterally loaded monopile are subjected to complex stress variations, which gradually evolve towards steady stress cycles as the cyclic lateral pile loading proceeds. The amplitude, direction and average value of such steady stress cycles are dependent on the depth and radial distance from the pile of the soil element, but it also invariably involves the cyclic rotation of principal stress axes. Complementary laboratory testing using the hollow-cylinder torsional apparatus was carried out on granular soil samples imposing cyclic stress paths (with up to about 3 × 104 cycles) which resemble those determined after 3D finite element analysis. The importance of considering the cyclic rotation of principal stress axes when investigating the response of soil elements under stress conditions mimicking those around a monopile foundation subjected to cyclic lateral loading is emphasised.

Effects of Fiber Stiffening to a Soft Actuator with PEDOT/PSS Electrode Films on Actuation Cycling Stability.

In this work, we fabricated a fiber-stiffened soft actuator with PEDOT/PSS films as electrode. Embedding nylon fibers in the soft actuator successfully suppressed twisting deformations, resulting in a large and persistent actuation displacement. We evaluated the effects of the fiber spacing (1, 2, 3 and 4 mm) on the displacement and assessed the actuation displacement as a function of applied voltage (0.5, 1.0 and 1.5 V) and frequency (0.2 and 1 Hz) with an actuation time of 500 s. We demonstrated that the fiberstiffened actuator with 2 mm fiber spacing exhibited steady actuation cycles (4.2 mm average displacement) in comparison with those with different spacings (1, 3, and 4 mm) and that without the fiber.

On the Workings of Tribal Politics

This paper tries to understand the workings of economies in which an (endogenous) subset of voters support certain (“tribal”) candidates regardless of their policies; and politicians choose whether or not to run on a tribal ticket. Two political regimes emerge. Non-tribal politics is characterized by centrist policies. Tribal politics produces extreme policies, typically from the right, despite the fact that the tribal base is from the lower middle class. Allowing policy in one period to determine the income distribution in the next, the economy either converges to a steady state or cycles between tribal and non-tribal regimes, depending on the vote share of the minority group, the scope for redistributive policy, and the salience of inter-group disparities.

Modeling the Nonlinear Dynamics of Intracellular Signaling Networks.

This protocol illustrates a pipeline for modeling the nonlinear behavior of intracellular signaling pathways. At fixed spatial points, nonlinear signaling dynamics are described by ordinary differential equations (ODEs). At constant parameters, these ODEs may have multiple attractors, such as multiple steady states or limit cycles. Standard optimization procedures fine-tune the parameters for the system trajectories localized within the basin of attraction of only one attractor, usually a stable steady state. The suggested protocol samples the parameter space and captures the overall dynamic behavior by analyzing the number and stability of steady states and the shapes of the assembly of nullclines, which are determined as projections of quasi-steady-state trajectories into different 2D spaces of system variables. Our pipeline allows identifying main qualitative features of the model behavior, perform bifurcation analysis, and determine the borders separating the different dynamical regimes within the assembly of 2D parametric planes. Partial differential equation (PDE) systems describing the nonlinear spatiotemporal behavior are derived by coupling fixed point dynamics with species diffusion.

ASSESSMENT OF FUEL AND ECOLOGICAL EFFICIENCY OF EXPLOITATION PROCESS OF RECIPROCATING ICE OF POWER PLANTS WITH CONSIDERING OF EMISSION OF BENZO(A)PYRENE AND POLYCYCLIC AROMATIC HYDROCARBONS

In this study, the author has improved its previously proposed methods for determining the value of mass hourly emi­s­sions of benzene(a)pyrene and polycyclic aromatic hydrocarbons in diesel engine ex­ha­ust gases flow. The purpose of the study is to obtain the values of complex fuel-ecological cri­terion that charac­te­ri­ze the ecological safety level of diesel engine exploitation pro­cess considering the emissions of benzo(a)py­rene and polycyclic aromatic hyd­rocar­bons as toxic and carcinogenic pollutants. The distributions of such emissions have been obtained over the field of a 2Ch10.5/12 auto­tractor diesel engine operating modes field and over the modes of stan­dardized ste­a­dy testing cycle ESC. The mathema­ti­cal apparatus and method of applica­ti­on of complex fu­el-ecological criterion of Prof. Igor Par­sadanov have been impro­ved. The author has obtained the distributions of these indicator values of eco­­logical safety level of power plants with reciprocating ICE exploitation process over the field of 2Ch10.5/12 autotractor diesel en­gine operating modes of and over modes of stan­dardized steady testing cycle ESC, as well as its average operating value. It has been establi­shed that, average operating values of Kfe criterion and the δKfe effect for all investigated va­riants of accounting for mass hourly emissions of B(a)P and PAH in die­sel engine exhaust gas flow are almost iden­tical and reduce the value of the Kfe crite­ri­on on 29 – 32 % – from 63 ‰ up to 42 – 45 ‰. The scientific novelty of the obtained results is that the approach of Prof. Igor Parsa­da­nov for criteria-based assessment of fuel-ecological effici­en­cy of au­to­tractor di­esel engines ex­plo­itation pro­cess as a part of power plant considering the of mass hourly emissions of benzo(a)­pyrene and po­ly­cyclic aro­matic hydrocarbons with RICE EG flow as the toxic pollutants and also methods for de­ter­­mi­ning of such emi­s­sions and ponderability of such pol­lutants received further development towards in direction of application of this mathe­ma­ti­cal apparatus for standar­di­zed steady testing cycles.

Bifurcation analysis in the system with the existence of two stable limit cycles and a stable steady state

Van der Pol–Duffing oscillator, which can be used a model for many dynamical system, has been widely concerned. However, most of the systems by scholars are either stable steady states or limit cycles. Here, the self-sustained oscillator with the coexistence of steady state and limit cycles, which is famous for describing the flutter of airfoils with large span ratio in low-speed wind tunnels, is treated in this paper. Using the energy balance method, the deterministic bifurcation of the tristable system with time-delay feedback is investigated. The presence of time-delay feedback expands the bifurcation range of the parameters, making the bifurcation phenomenon more abundant. In addition, according to the stationary probability density function obtained by the stochastic averaging method, stochastic bifurcation of the system with time-delay feedback and noise is explored theoretically. The numerical results confirm the correctness of the theoretical analysis. Transition between the unimodal structure, the bimodal structure and the trimodal structure is found. Many rich bifurcations are available by adjusting the time-delay and noise intensity, which may be conductive to achieve the desired phenomenon in the real-world application.

Correlation-induced steady states and limit cycles in driven dissipative quantum systems

We study a driven-dissipative model of spins one-half (qubits) on a lattice with nearest-neighbor interactions. Focusing on the role of spatially extended spin-spin correlations in determining the phases of the system, we characterize the spatial structure of the correlations in the steady state, as well as their temporal dynamics. In dimension one we use essentially exact matrix-product-operator simulations on large systems, and pushing these calculations to dimension two, we obtain accurate results on small cylinders. We also employ an approximation scheme based on solving the dynamics of the mean field dressed by the feedback of quantum fluctuations at leading order. This approach allows us to study the effect of correlations in large lattices with over one hundred thousand spins, as the spatial dimension is increased up to five. In dimension two and higher we find two new states that are stabilized by quantum correlations and do not exist in the mean-field limit of the model. One of these is a steady state with mean magnetization values that lie between the two bistable mean-field values, and whose correlation functions have properties reminiscent of both. The correlation length of the new phase diverges at a critical point, beyond which we find emerging a new limit cycle state with the magnetization and correlators oscillating periodically in time.

A mathematical model for the role of macrophages in the persistence and elimination of oncolytic viruses

Replicating oncolytic viruses provide promising treatment strategies against cancer. However, the success of these viral therapies depends mainly on the complex interactions between the virus particles and the host immune cells. Among these immune cells, macrophages represent one of the first line of defence against viral infections. In this paper, we consider a mathematical model that describes the interactions between a commonly-used oncolytic virus, the Vesicular Stomatitis Virus (VSV), and two extreme types of macrophages: the pro-inflammatory M1 cells (which seem to resist infection with VSV) and the anti-inflammatory M2 cells (which can be infected with VSV). We first show the existence of bounded solutions for this differential equations model. Then we investigate the long-term behaviour of the model by focusing on steady states and limit cycles, and study changes in this long-term dynamics as we vary different model parameters. Moreover, through sensitivity analysis we show that the parameters that have the highest impact on the level of virus particles in the system are the viral burst size (from infected macrophages), the virus infection rate, the M1$\to$M2 polarisation rate, and the M1-induced anti-viral immunity.

Carbon-Coated Yttria Hollow Spheres as Both Sulfur Immobilizer and Catalyst of Polysulfides Conversion in Lithium-Sulfur Batteries.

Li-S battery has tremendous application prospect on account of the high theoretical specific capacity and large energy density, while its large-scale application is impeded by the severe shuttle effect and the slow electrochemical kinetics of polysulfides conversion. Herein, the Lewis acidic yttria hollow spheres (YHS) are rationally designed as both sulfur immobilizer and catalyst of polysulfides conversion for the advanced Li-S batteries. It can be known that the Lewis acidic yttria can effectively capture the Lewis basic polysulfides and thus mitigate the shuttle effect of Li-S battery; besides, yttria shows the enhanced catalytic effect for the kinetics of interconversion reaction from polysulfides to Li2S. As a result, either as a sulfur host or as the separator coating, yttria plays a vital part in realizing the high specific discharge capacity and good cycle stability for Li-S battery. In particular, Li-S battery with YHS@C/S cathode and YHS/CNT-0.6- modified separator (2.1 mg cm-2 active material loading) shows a good specific discharge capacity of 912.5 mAh g-1 at 0.5C. Even after 200 steady cycles, the discharge specific capacity can keep as 842.3 mAh g-1, and the capacity decay rate is only 0.038% per cycle. When active material areal loading is increased to 4.24 mg cm-2, it still maintains a considerable areal capacity of 3.79 mAh cm-2. In consequence, the synergy of polysulfides confinement and catalytic conversion reaction provides a meaningful exploration for achieving the high performance of Li-S batteries.

Fuel cycles with PK-3+ FAs for VVER-440 reactors

Abstract In order to increase the efficiency of fuel utilization at Dukovany NPP, the design of FA was changed by shroud removal and replacement with a structure called “Karkas”. Optimization of PK-3+ type FAs with different average enrichments was performed in order to find out those enrichment profiles with minimized non-uniform energy generation in FA (during burn-up). In addition, it was assumed that such a radial enrichment profile in FA could be achieved by making a change in the location of the fuel pin with a Gd2O3 burnable absorber – from the 2nd row to the 3rd row of pins from the edge of the fuel assembly on the fuel assembly diagonal. The aim of this study was to achieve a full quadruplicate cycle, every 15 months (approx. 450 days) at 1475 MWt nominal power. Preliminary results indicate that combination of PK-3+ and Gd-2M+ fuel assemblies does not show any unusual phenomena from the point of view of reactor physics. The proposed strategy is based on B1C33 cycle implemented at Dukovany NPP that is designed to be 395 FPDs. Already in the first “transient” cycle (34th) loaded with 60 fresh PK-3+ FAs and 12 Gd-2M++ CAs, the reached length at EOR is 424 FPDs, which means stretch-out 26 effective days. Averaged, the transition cycle stretch-out length is 23.5 effective days. For steady cycles, this average value is 19.2 effective days.

How Spatial Heterogeneity Affects Transient Behavior in Reaction-Diffusion Systems for Ecological Interactions?

Most studies of ecological interactions study asymptotic behavior, such as steady states and limit cycles. The transient behavior, i.e., qualitative aspects of solutions as and before they approach their asymptotic state, may differ significantly from asymptotic behavior. Understanding transient dynamics is crucial to predicting ecosystem responses to perturbations on short timescales. Several quantities have been proposed to measure transient dynamics in systems of ordinary differential equations. Here, we generalize these measures to reaction-diffusion systems in a rigorous way and prove various relations between the non-spatial and spatial effects, as well as an upper bound for transients. This extension of existing theory is crucial for studying how spatially heterogeneous perturbations and the movement of biological species involved affect transient behaviors. We illustrate several such effects with numerical simulations.

Experimental and bifurcation analysis of a hybrid CSTR plant

The classical continuous stirred tank reactor (CSTR) with an exothermic chemical reaction is known for its complex nonlinear behaviour. Therefore, it is often used as a benchmark plant for testing control algorithms. Since experimenting with a real chemical process can be dangerous (thermal runaway), computer simulations can be used in the controller design. On the other hand, simulation results are obtained for mathematical models that often include many simplifying assumptions. Hence, the goal of this study was to design a hybrid CSTR (hCSTR) plant with real reactor vessel and jacket, but simulated chemical reaction. Based on bifurcation analysis and laboratory experiments, it is shown that the hCSTR plant exhibits the same qualitative behaviour (multiplicity of steady states and limit cycles) as the classical CSTR system. The analysis is performed assuming hard-saturation constraints on the reaction heat, since the heating power in the real hybrid plant is also constrained. Finally, a proportional-integral (PI) controller for stabilization of temperature in the vessel is designed and tested by using the hCSTR plant.

Carbon allowance allocation in the shipping industry under EEDI and non-EEDI

The CO2 emissions targets in this study are based on the Paris Agreement, which aims to cut emissions in 2050 to half of the 2005 levels, with a focus on the shipping industry. This study uses data for various kinds of vessels following the guidelines set in the Energy Efficiency Design Index (EEDI) and examines emission levels and the results of using different strategies during three different business climates. Carbon allowance allocations and cost benefit ratios (CBR) are included. The results show that the minimal free carbon allowances in 2050 for vessels in keeping with EEDI or non-EEDI scenarios should be set so that (1) under prosperous business cycles they are 29% and 14%; (2) under steady business cycles 83% and 42%; (3) under sluggish business cycles 510% and 255%, respectively. In addition, when shipping companies follow the emission cap guidelines, the CBR in 2050 for vessels in both scenarios will be (1) 37.52% and 47.45% during prosperous business cycles; (2) 43.49% and 45.65%during steady business cycles; (3) and 53.60% and 53.83% during sluggish business cycles, respectively. The results indicate that during prosperous business cycles, although the free carbon allowance for shipping companies will be greatly insufficient, their profits will still be higher than during sluggish business cycles.